1. Field of the Invention
The present invention is related to speaker simulators that utilize mechanical systems to simulate the distortion to a sound system caused by a speaker cabinet.
2. Prior Art
The sounds of electrically amplified instruments are greatly affected by the associated amplification circuitry and speakers, i.e., the amplifier/speaker system. In fact, many rock musicians have strong preferences for certain types of amplifier/speaker systems for their effects on musical signals. For instance, many rock guitarists prefer amplifiers which use tube circuitry rather than solid state circuitry since the distortion produced by tubes differs from that produced by transistors. Rock musicians also tend to prefer certain brands of amplifier/speaker systems for the characteristics which these systems add to the sound. Furthermore, many musicians prefer the sound characteristics added to a musical signal when an amplifier/speaker system is generating a high volume output.
However, it is not always convenient to generate loud music through an amplifier/speaker system, or to monitor the output of the amplifier/speaker system through a microphone. For instance, in a recording session it is desirable to isolate the sounds produced by each musician so as to be able to control the final mix down. If many musicians are playing through loud amplifier/speaker systems then it becomes necessary to acoustically isolate the musicians. This can be technically difficult and unconducive to providing an ensemble feeling to the musicians.
When bands are performing in concert it is also technically difficult to monitor the output of the amplifier/speaker system of each musician while maintaining isolation between the systems. Some rock bands are known to run the output from the electrical instruments in the concert hall to large vans parked outside where the music is played through an amplifier/speaker system, monitored with a microphone, and brought back into the concert hall for a final stage of amplification before being played over the loudspeakers. Such measures are of course expensive and inconvenient.
To generate a signal impressed with the characteristics of a loud amplifier/speaker system while producing a minimum amount of noise some manufacturers, such as Demeter of Santa Monica, Calif., have introduced sound insulating enclosures which contain speakers and a microphone. When the speakers are producing high volume acoustical signals the microphone signal has the characteristics of sounds produced by a loud sound system. However, a minimum amount of sound leaks from the enclosure. Disadvantages of this system include the added expense of a sound insulating enclosure and a microphone, and the unnatural effect of the short delay times from reverberations of the sound off the inside walls of the enclosure.
Other manufacturers provide electrical sound processing systems which simulate the characteristics of loud amplifier/speaker systems using digital electronics. Because of the complexity of the characteristics of amplifier/speaker sound systems, such simulation systems are somewhat inadequate. Distortion effects produced by speakers include: "driving force distortion" produced by the movement of the voice coil out of the homogeneous region of the field produced by the magnet; "support system distortion" produced by nonlinearities in the elasticity of the suspension system for the speaker cone; "air distortion" produced by the nonlinearity in the compressibility of air at high pressures; and "frequency-modulation distortion" produced by the low-frequency motion of the speaker cone affecting the high-frequency output of the cone. Since these types of distortion are nonlinear they cannot be simulated by digital techniques such as linear filtering.